Method of preventing cleaned metal from rusting



Patented Dec. 12, 1933 UNITED STATES METHOD OF PREVENTING CLEANED METAL FROM RUSTING James H. Gravel], Elkins Park, Pa., aesignor to American Chemical Paint Company, Ambler, Pa., a corporation of Delaware No Drawing. Application November 20, 1928 Serial No. 320,750

7 Claim.

This invention relates to the art of preventing metal from rusting, and although it may have a wide scope, it is particularly applicable to preventing steel cleaned with acid from becoming stained with rust.

The objects of the invention are to prevent steel that has been cleaned from rusting; to prevent rust stains from appearing on a steel surface that has been cleaned with acid; to keep a cleaned steel surface free from corrosion during the interval between cleaning and painting; to produce a pickled steel surface free from lime that will not show signs of rust for long periods and to generally improve the art of preventing cleaned metal from rusting.

Generally stated the invention consists in coating the cleaned metal with a film of metallic arsenic. I have found this may be accomplished by treating the cleaned metal with a liquid solution of an arsenic compound, which by double decomposition, dissolves a portion of the steel surface, and in its place, deposits a film of metallic arsenic. One of the best materials for the purpose is sodium arsenite. This may be produced by dissolving arsenious oxide in an aqueous solution of sodium hydroxide.

After the film of arsenic has been developed the metal may remain, under ordinary indoor atmospheric conditions, for long periods without showing the development of rust. However, the film-forming chemical, if not removed after accomplishing its objects, dries on the metal and detracts from its appearance, and in case the metal is to be painted, leaves a surface that is not considered suitable for receiving the painted finish. Under these conditions the arsenic solution should be removed after accomplishing its purpose. This can be accomplished by washing the metal with water, which will remove the 0 liquid chemical, without removing the film of metallic arsenic that has been deposited on the metal. The washing willalso remove the deleterious products of the solution's reaction, such as salts of iron, etc.

Although the invention may be employed on metal cleaned by any method, as for example, filing, rubbing, buiiing, etc., it is especially useful where the metal has been cleaned by subjecting it to the action of an acid, as for example. in pickling, cleaning with admixtures of an acid and an alcohol-like material, etc.

When acids are used for cleaning the metal, it is well to remove all traces of acid, before subjecting the metal to my rust-preventing step, in 55 the cleaning process. This may be done by washing the acid-cleaned metal with water, but when the acids are of a highly corrosive nature, as for example, sulphuric acid and hydrochloric acid, it

it well, after the washing operation, to subject the metal to the action of an alkaline material, such as lime-water, to neutralize all traces of acid left behind after the washing operation, and then remove the coating of lime left on the metal by again washing with water.

I will now describe several ways of commercially using my method.

The metal is cleaned by machining it so that the surface presents true clean metal. It is then treated with an admixture of arsenious oxide (AS203), sodium hydroxide (NaOI-l) and water, compounded'in the following proportions:

Water 0.9420 gallons Sodium hydroxide 1.3300 pounds Arsenious oxide 1.6650 pounds It is found in practice that the concentration of the arsenic is much greater than that actually required, hence the above admixture may be diluted with water, where economy is a factor, to the extent of one part by volume of the admixture and one hundred parts by volume of water.

This admixture may be applied with a swab or the metal may be dipped into the admixture. After the admixture has been in contact with the metal for a few moments, say three minutes, more or less, the metal is washed with water and permitted to dry.

In cases where the metal has been cleaned with an admixture of phosphoric acid and a solvent, like alcohol; after the metal has been cleaned to satisfaction, and before the acid admixture has had time to dry on the metal, I wash the metal with water, and before the metal has had time to dry, I treat it with my admixture, either strong or dilute, and then wash it with water and permit it to dry. As the surface produced is free from tarnish, it affords a desirable surface on which to apply a finishing coating, like paint, lacquer, japan or varnish.

When applying my method in the usual pickling of steel, the metal is pickled in a dilute solution of sulphuric acid to remove the scale, and then washed with water and treated with my admixture, which, in this case, is made in the form of a bath. After'immersing the metal in this bath, it is washed with water and permitted to dry. This produces pickled metal which remains unrusted for relatively long periods, yet is not disfigured by an unsightly coating of lime, which is usual in ordinary pickling where the pickled metal is treated with a lime bath to prevent the pickling acid from causing the cleaned metal to rust. Where it is not considered advisable to change the regular pickling procedure, which consists in pickling in a bath of sulphuric acid, washing in water and neutralizing in a bath of lime water, I wash the lime from the metal before it has had an opportunity to dry on the metal, and then immerse the metal in a bath of my admixture, using approximately one part of the admixture to one hundred parts of water, by volume, and then permit the metal to dry. After which, the metal may be given an oil or other weatherproof coating.

I claim:

1. The method of preventing cleaned ferrous metal from rusting, comprising coating the cleaned metal with a film of metallic arsenic, by treating it with a liquid of sodium arsenite.

2. The method of preventing cleaned ferrous metal from rusting, comprising coating the cleaned metal with a film of metallic arsenic, by treating it with a liquid admixture comprising sodium hydroxide and arsenious oxide.

3. The method of preventing ferrous metal cleaned with acid from rusting, comprising removing the material used for cleaning, from the cleaned metal and coating the cleaned metal with a film of metallic arsenic.

4. The method of preventing ferrous metal cleaned with acid from rusting, comprising removing the acid used for cleaning, from the cleaned metal, and coating the cleaned metal with a film of metallic arsenic, by subjecting the cleaned metal to the action of a liquid solution of an arsenic compound.

5. The method of preventing ferrous metal cleaned with acid from rusting, comprising cleaning the metal by subjecting it to the action of an acid, removing the cleaning acid from the cleaned metal by first washing the metal with water, and then treating it with an acid neutralizing material, removing the neutralizing material and coating the metal so treated with a film of metallic arsenic, by subjecting the metal to the action of a liquid solution of an arsenic compound.

6. The method of preventing ferrous metal cleaned with acid from rusting, comprising subjecting the metal to a dflute solution of sulphuric acid to clean the metal, removing the dilute solution of sulphuric acid by first washing the cleaned metal with water, and then treating it with lime water, removing the lime water from the metal by washing with water, and subjecting the metal to the action of a liquid solution of an arsenic compound.

7. The method of preventing cleaned ferrous metal from rusting, comprising coating the cleaned metal with a film of metallic arsenic, by subjecting it to the action of an admixture comprising water, sodium hydroxide and arsenious oxide.

JAMES H. GRAVELL. 

